Sabine Hossenfelder, a physicist at the Frankfurt Institute for Advanced Studies in Germany, and Tim Palmer, a Royal Society Research Professor of Climate Physics at the University of Oxford, write:
In a recent column in Scientific American, Naomi Oreskes argues that we understand the physics of climate change well enough now. She writes that the scientists of the Intergovernmental Panel on Climate Change’s (IPCC’s) Working Group 1 (WG1)—the ones tasked with assessing the physical science basis of climate change—should “declare their job done.” According to Oreskes, we should instead now deal with the problem by focusing on adaptation and mitigation.
It is true that the scientific basis of global long-term trends is settled. We know that sea levels are rising, average temperatures are increasing, and glaciers are dying. We know that business as usual will put our and future generations at risk of great suffering. But we do not have a good understanding of the regional impacts of climate change, and uncertainties in the long-term predictions currently span a range that could mean anything from a serious but manageable inconvenience to an existential threat.
Indeed, Oreskes has previously been critical of WG1’s reports: a February 2013 paper she co-authored in Global Environmental Change argued that the IPCC reports have consistently underpredicted ”at least some of the key attributes of global warming from increased atmospheric greenhouse gases.” But why is that? It’s because the job of climate scientists is not done.
A key reason for the underestimates that Oreskes and her colleagues belabored is that current-generation climate models are crude representations of the complex dynamical system that is our climate. For example, current global climate models can’t represent cloud systems using the laws of physics because the grid spacing is too coarse (a hundred kilometers or more). In the models, therefore, clouds are represented by highly simplified empirical formulas that describe the clouds’ true properties in a relatively crude way.
But clouds are a vital part of the global hydrologic cycle and therefore play a key role, not only in determining the magnitude of global warming but also in shaping extreme weather events around the world. Because of the simplified representations of clouds, current climate models tend to systematically misplace the principal regions in the tropics, known as the intertropical convergence zones, where rainfall occurs. In midlatitudes, the models underestimate the number of long-lived high-pressure systems known as anticyclones, which are associated with heat waves, forest fires and drought. All of these errors are typically at least as large as the climate-change signals the models attempt to simulate.
The consequence of our inability to model essential climate processes very accurately is that we cannot correctly simulate extreme weather and climate events. The horrendous weather events of 2021—the near-50-degree-Celsius heat in British Columbia and the devastating flooding in the Eifel region in Germany, China’s province of Henan and New York City—are completely outside the range of what current-generation climate models can simulate.
This in turn means that, at the moment, we cannot quantify the extent to which such extreme events were caused by climate change. Despite this, weather event attribution has attracted a lot of attention in recent years, particularly in the media. For such attribution, climate scientists run climate models twice, once with the observed current-day levels of carbon dioxide and once with preindustrial levels. Using these runs, they attempt to estimate how the likelihood of a particular type of weather event changes as a result of our carbon emissions.
But because current climate models cannot correctly simulate any of the extreme events of 2021 with their observed intensity, we cannot actually estimate how much the probability of these events increased—we just get a meaningless likelihood ratio of 0:0. Therefore, to estimate the probability, one has to look at less extreme events that have a higher probability of occurring than those that actually took place. As a result, the estimate one gets for how much the probability of extreme events has increased might be orders of magnitude too low. Perhaps these events were 50 percent more likely because of climate chance; perhaps they were 50,000,000 percent more likely—we can’t tell. The science of extreme event attribution is far from done and dusted. Indeed, it has hardly begun.
More important than quantifying what is happening now is quantifying what is about to happen. Countries will need sound model projections to prioritize adaptation strategies. If climate change could bring enhanced flooding and storminess on the one hand and stronger heat waves and drought on the other, how should money be spent most effectively to make a nation more climate resilient? We can’t answer this question if we can’t accurately quantify the likelihood of these alternative scenarios.
Further, we need reliable models if we are ever to take climate geoengineering seriously. If we one day consider spraying artificial aerosols in the stratosphere as a way to offset global warming, we need models to tell us what this would do, say, to the rainfall patterns associated with the Asian summer monsoon.
To add one final reason, we also need better models to understand how changing wind and cloud patterns will affect our electricity production by renewables later this century. We do not know, for example, whether to take seriously the possibility of “global stilling,” the idea that, because of Arctic warming, the pole-to-equator surface temperature gradient is weakening, leading to a reduction in Northern Hemisphere midlatitude wind systems. So how are we to decide whether wind turbines are a good investment?
In short, to address fundamental issues in climate mitigation, adaptation and geoengineering—the sorts of things Oreskes says we should now focus on—we need to understand the physical basis of climate much more quantitatively than we currently can. Research on basic science and downstream solutions should develop hand in hand.
To confront these problems and pool resources, the world needs to come together to create a federated international center for climate change, a sort of “CERN for climate change.” Each arm of the federation would have state-of-the-art exascale computers. Here, scientists could develop a new generation of ultra-high-resolution climate models with a grid spacing around one kilometer—an improvement that would greatly alleviate the shortcomings of current models by reducing the need for these empirical formulas and instead allowing small-scale processes to be represented by the basic laws of physics. Instead of hanging up their boots, WG1 would then be able to provide a much clearer picture of how climate change will manifest itself.
Climate change has all the makings of an unfolding global disaster, yet scientists still have much to understand. Claiming that the science is done when it isn’t, risks that more people will die because they weren’t prepared for what was to come.
Naomi Oreskes, a professor of the history of science at Harvard University, replies:
Hossenfelder and Palmer object to the suggestion that there might be a case for less climate science, but they misunderstand my argument. I am not calling for an end to climate science. I am calling for wrapping up a particular project that has achieved its ends.
Science as a process of learning and discovery is never done. From our current vantage point, early-20th-century pronouncements that physics was finished (on the eve of the relativity and quantum mechanics revolutions) look preposterous. So do late-20th-century declarations of the “end of science.” But history shows that particular lines of inquiry have ended as scientists concluded that they were misguided (phrenology), unachievable (specific short-range earthquake prediction) or answered (the link between smoking and cancer).
My argument is not that climate science is done; it is that scientists have answered the question that was posed to them in the 1992 United Nations Framework Convention on Climate Change: What level of anthropogenic interference constitutes “dangerous anthropogenic interference” with the climate system? The answer, encapsulated in a recent IPCC report and WG1’s latest assessment, is warming at or above 1.5 degrees C. When you have answered a question, the next thing to do is stop.
Moreover there is a cost to not stopping: large assessments consume huge amounts of scientific time and energy, not to mention leaving heavy carbon footprints. Michael Oppenheimer, a climate scientist long involved in the IPCC, estimates that about one quarter of his working time over the past decades has been dedicated to IPCC reports. Multiply that by the thousands of scientists who work on any single IPCC assessment, and you’ve got tremendous time and labor not spent on other scientific challenges and a huge amount of energy-consuming travel. Large ongoing assessment reports also send a mixed message to the public: that the science is at the same time “unequivocal” and in need of further evaluation. That doesn’t help the cause of public understanding. And the appraisals take such a long time to produce, noted climatologist Kevin Trenberth, who has been a lead author on several IPCC scientific reports, that by the time they come out they may not be quite up-to-date.
Should scientists continue to improve climate models so that we can better understand climate feedbacks and forecast the effects of our interventions? Should scientists continue to work to improve our understanding of climate impacts on the regional and local level and their relation to extreme weather events? Do we need better data on wind and cloud patterns as we transition to a renewable-energy economy? Yes, yes and yes. (I have long argued that better understanding of regional and local effects is essential to planning for adaptation.) The question is not “Do we need this science?” The question is whether yet another big assessment is the best route to it.
To the scientists who have done the job they were asked to do, I say: Thank you! Declare victory and pass the baton to the experts in the social, political and economic questions essential to finding and implementing effective solutions to the climate crisis. Doing so would not only be a service to the world; it would be a service to science as well.